How do you drive a robot you can never reach?

Before any rover can drive, it has to get there. Earth and Mars both circle the Sun, Earth faster. Pick a launch date and send the ship out on the cheapest path, a long coast that takes about eight and a half months. Mars has to be waiting where the ship arrives.

The ship hits the top of the Martian air at about 20,880 km/h. About seven minutes later the rover must be standing on the ground. On Perseverance's landing day a radio signal took 11 min 22 s to reach Earth, so by the time anyone hears that the landing has begun, it is already over. Set the four steps before you arrive: nobody can change them after that.

The rover is down. The rock you want to study is about half a kilometre away, across a field of boulders. First try driving it live: every command takes between 3 and 22 minutes to arrive, and every picture takes as long to come back. Then plan a whole sol at once, the way rover drivers really work.

Curiosity and Perseverance carry a laser on their mast. It fires at a rock up to 7 m away and turns a speck smaller than a pinhead into a spark of glowing gas. Every chemical element glows at its own colours, so the spark's light tells you what the rock is made of. Pick a target, fire, and decide whether water ever moved through it.

Perseverance carried a passenger: Ingenuity, a helicopter of just 1.8 kg. A helicopter lifts itself by pushing air down, and Mars has very little air to push. Its air is about 1% as dense as Earth's. Choose how fast the rotors spin, then let it fly its hop.